JSON for Modern C++ vs TOON
Which should you use? A side-by-side look at what each one does, who it suits, what it costs, how hard it is to set up, and where each falls short.
Open source · MIT
A single-header C++ library for reading, writing and manipulating JSON data.
Open source · MIT
A compact, human-readable way to write JSON data for LLM prompts, with a TypeScript SDK and CLI.
The short answer
Choose JSON for Modern C++ if you need…
- C++ developers who need to read or write JSON in an application
- Teams that want a library with no dependencies and a simple header-based setup
- Projects that prioritize ease of use over raw parsing speed
- Developers who want JSON Patch or JSON Pointer support in C++
Choose TOON if you need…
- Developers who send structured JSON data to LLM prompts and want to reduce token usage
- Teams using TypeScript who want an SDK to encode and decode the format
- People who want to measure token savings with the included benchmarks
- Anyone converting JSON files to TOON from the command line
Side-by-side
| JSON for Modern C++ | TOON | |
|---|---|---|
| Type | Library | Library |
| Price | Free and open source | Free and open source |
| Licence | MIT | MIT |
| GitHub stars | 50.8k | 25.6k |
| Setup difficulty | Beginner | Beginner |
| How you get it | Clone and build from source | Install with a package manager |
| Main language | C++ | TypeScript |
| Last code update | 4 days ago | 5 days ago |
What each one is
JSON for Modern C++
nlohmann/json is a C++ library that lets programs work with JSON data using familiar C++ containers and operators, so JSON objects and arrays can be handled much like std::map and std::vector. It is distributed as a single header file, which makes it simple to add to a project. The README also mentions support for related formats such as CBOR, MessagePack and BSON, plus JSON Pointer and JSON Patch.
TOON
TOON (Token-Oriented Object Notation) is a text format that represents JSON data in fewer characters, so it takes up fewer tokens when you paste it into a large language model prompt. It is meant to stay readable by humans. The project provides a TypeScript SDK, a command-line tool, and benchmarks comparing it with JSON.
Best for
JSON for Modern C++
- C++ developers who need to read or write JSON in an application
- Teams that want a library with no dependencies and a simple header-based setup
- Projects that prioritize ease of use over raw parsing speed
- Developers who want JSON Patch or JSON Pointer support in C++
TOON
- Developers who send structured JSON data to LLM prompts and want to reduce token usage
- Teams using TypeScript who want an SDK to encode and decode the format
- People who want to measure token savings with the included benchmarks
- Anyone converting JSON files to TOON from the command line
Strengths
JSON for Modern C++
- Single header file with no dependencies, according to the README
- Intuitive syntax that feels close to native C++ containers
- Heavily unit-tested with fuzzing via Google OSS-Fuzz and MIT licensed
TOON
- Aims to reduce token count for JSON data sent to language models
- Stays human-readable, so people can inspect the data directly
- Ships with an SDK, a CLI, and benchmarks in one repository under the MIT license
Not ideal for
JSON for Modern C++
- Projects that need the fastest possible JSON parsing, since the README says faster libraries exist
- Developers not working in C++, because this library is for C++ only
- Projects that must avoid a large single header file in build times, as the README does not discuss compile-time cost
TOON
- Projects that only exchange data between services and do not use LLMs, since the format's main benefit is for prompts
- Users who need a format with broad support across many languages, since the README describes a TypeScript SDK and the other language support is unclear from the provided text
Trade-offs
JSON for Modern C++
- The README says it is not the fastest JSON library available
- Documentation and examples are primarily hosted on an external site, so the README alone gives limited detail
- The README is truncated, so some features and setup details could not be verified here
TOON
- The benefit depends on the data and the model's tokenizer; savings are not guaranteed for every dataset
- Adopting a new format means your prompts and tooling must handle TOON rather than standard JSON
- The README was truncated, so details on the full specification and language support are not confirmed here
Getting started
JSON for Modern C++
Clone the repository
git clone https://github.com/nlohmann/json.gitFrequently asked questions
What is the difference between JSON for Modern C++ and TOON?
JSON for Modern C++: A single-header C++ library for reading, writing and manipulating JSON data. TOON: A compact, human-readable way to write JSON data for LLM prompts, with a TypeScript SDK and CLI. JSON for Modern C++ suits c++ developers who need to read or write json in an application, while TOON suits developers who send structured json data to llm prompts and want to reduce token usage.
Are JSON for Modern C++ and TOON free?
JSON for Modern C++: Free and open source. TOON: Free and open source.
Is JSON for Modern C++ or TOON more popular?
JSON for Modern C++ has more GitHub stars (50.8k) than TOON (25.6k). Popularity isn't the same as fit — check which one matches your use case above.
What are other alternatives to JSON for Modern C++ and TOON?
Other options people compare them with include SwiftyJSON, GJSON, cpp-httplib, EnTT, store.js.
Keep comparing
Built from our catalogue entries for both products: open-source details come from each project's README (AI-assisted, refreshed weekly) and GitHub data; AI-tool details are editorial. Spotted something wrong? Let us know from either product's page.